drm/exynos: Use the new event init/free functions

drm/exynos: Use the new event init/free functions

Also fixes a bug in IPP with not correctly checking/allocating for
space in the event space. Not a too serious bug since it's not a
real ringbuffer, just a limit to avoid too much kernel allocations.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Inki Dae <inki.dae@samsung.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452548477-15905-4-git-send-email-daniel.vetter@ffwll.ch
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>